This invention relates to a magnetic recording medium and a process for preparing the same, and particularly to a thin metal film-type magnetic recording medium having a large perpendicular magnetic anisotropy and a process for preparing the same.
High density magnetic recording media can be made by forming a ferromagnetic thin film composed of such a metal as Co, Fe or Ni, or their alloy on a non-magnetic substrate by so-called physical vapor deposition such as vacuum evaporation, sputtering or ion plating. The thus obtained surface-coated, non-magnetic substrate is used as a magnetic recording medium. Particularly from such a perpendicular magnetic recording medium wherein magnetic domain is formed in a direction perpendicular to the film surface of the magnetic recording medium, a very high magnetic recording density such as 100 K bits per inch or more can be obtained.
The conventional perpendicular magnetic recording medium is disclosed in IEEE Trans. Magnetics, MAG 20, No. 5 (1984), pp 657-662, and it is necessary that a magnetic recording medium for use in perpendicular magnetic recording has so-called perpendicular magnetic anisotropy so that magnetization is liable to occur in a direction perpendicular to the film surface. The well known magnetic films having such properties include films of Co-based alloys such as Co-Cr, Co-Re, Co-V, Co-Mo, Co-Ta, etc. The films of these alloys can be formed on non-magnetic substrates by physical vapor deposition, but still have such problems that the perpendicular magnetic anisotropy of a magnetic film is reduced, or in a worst case, is lost, depending upon the apparatus and conditions for forming the film.
The magnetic properties of a magnetic recording medium depend upon various factors such as the composition of a magnetic film, a process for forming the film, and a substrate temperature and a film-forming rate during the formation of the film. Another factor having a large influence upon the magnetic properties is a gas atmosphere during the formation of a magnetic film, but no thorough investigation has been so far made as to this factor, and thus there is still a problem that magnetic films having good perpendicular magnetic anisotropy cannot be prepared with good reproducibility.